Three-Dimensional Organization of the Hepatic Microvasculature in Hereditary Hemorrhagic Telangiectasia.
The affected livers of patients with HHT show complex abnormalities of the hepatic vasculature with irregular fibrosis.[4,5] Three kinds of vascular shunts occur in the liver and correlate closely with the clinical features. Arteriovenous (A-V) shunts result in left-to-right shunting, terminating in high-output congestive heart failure; portovenous (P-V) shunts cause hepatic encephalopathy; and arterioportal (A-P) shunts result in portal hypertension.
The pathology of the hepatic involvement in HHT patients is poorly understood, since investigators have examined only 1 to 4 cases of HHT in each study.[4,5] Martini reviewed 14 reported cases with HHT and classified them into 3 subgroups according to their hepatic histopathologic features: telangiectasia with fibrosis or cirrhosis (group 1), cirrhosis without telangiectasia (group 2), and telangiectasia without fibrosis or cirrhosis (group 3). The cirrhosis in some patients of group 2 seemed to be related to superimposed liver diseases, particularly posttransfusion hepatitis. Daly and Schiller analyzed 4 cases and concluded that randomly scattered fibrovascular lesions were pathognomonic for livers with HHT. They observed 3 histologic patterns of lesions: (1) a honeycomb meshwork of dilated sinusoidal channels; (2) tortuous, thick-walled veins flanked by numerous wide-caliber arteries that course randomly through the parenchyma amid variable amounts of fibrous tissue; and (3) enlarged portal areas with numerous dilated vessels. Although these reports describe vascular abnormalities of affected livers, the pathologic changes responsible for formation of the intrahepatic shunts have barely been investigated.
To address this issue, we performed a 3-dimensional (3-D) reconstruction study of the hepatic microvasculature in a patient with HHT. To our best knowledge, this is the first report on 3-D reconstruction study of the hepatic lesions in HHT. Immunohistochemical study was also performed to identify the types of HHT.
We used a recent computer-assisted 3-D reconstruction method. Although the colored gelatin casts have commonly been used for the 3-D study of the vascular structures, this method requires extensive preliminary experiments and preparations. The new method is easy and applicable to routine paraffin sections. It can also analyze any histologic structures.
MATERIALS AND METHODS
The livers of a patient with HHT described herein and an 88-year-old woman (healthy control) were obtained at autopsy and used for the 3-D analysis. Paraffin blocks were prepared from 10% formalin-fixed liver tissue by a routine method. More than 200 serial sections (4 [micro]m thick) were stained with elastica van Gieson for identification of elastic fibers. Several areas of abnormal microvasculature were selected under the microscope and photographed at a magnification of X48. The pictures were enlarged to twice their original size, and transparencies were made. The portal areas were outlined by the limiting plates of hepatocytes, and then the hepatic arterial branches were identified by their distinctive internal elastic lamina and muscular media. The ectatic sinusoids and central veins have focal aggregations of elastic fibers in their walls close to the lumens, and the central veins can be distinguished from the ectatic sinusoids by larger diameters and the characteristic centripetal arrangement of the hepatocellular trabeculae. Thus, the types of microvasculature were identified under a microscope and then marked on the transparencies with color pens. The 3-D reconstruction was performed with the help of a personal computer (Gateway 2000, North Sioux City, SD). The outlines of the microvasculature on the transparencies were traced on a tablet, and the microvasculature was reconstructed using OZ for Windows version 1.0 software (Rise S. I. Corp, Ichikawa, Chiba, Japan).
The immunohistochemical study was performed by the streptavidin-biotin method using an LSAB (labeled streptavidin-biotin) kit (Dako Corporation, Kyoto, Japan). The paraffin sections were deparaffinized, hydrated, digested with 0.1% trypsin solution at 37 [degrees] C for 20 minutes, and pretreated with both avidin and biotin solutions for blocking endogenous biotin at 37 [degrees] C for 15 minutes. The primary mouse monoclonal antibody was anti-human endoglin (CD105) (M3527, clone SN6h, Dako) used at a 1: 500 dilution ratio. The catalyzed signal amplification method was used to enhance the signals, using a catalyzed signal amplification system kit (K1500, Dako), according to the manufacturer's protocol.
Written informed consent was obtained from the families of the objective cases at the time of autopsy. The use of autopsy materials for medical education and research is generally permitted in accordance with the Preservation of Autopsy Law of Japan.
REPORT OF A CASE
A 77-year-old Japanese woman was admitted to Tokyo Metropolitan Geriatric Hospital complaining of epigastralgia, nausea, and loss of appetite. She had a history of recurrent epistaxis that started in her 20s, and her mother and son also had recurrent episodes of epistaxis. She did not drink alcohol.
A-physical examination revealed multiple severe telangiectasia of the lips, face, anterior chest, and fingers. Serological test results for serum hepatitis B surface antigen and anti-hepatitis C virus (second generation) were negative. Her hematologic data disclosed severe anemia, with the following laboratory values: red blood cells, 2.59 X [10.sup.6]/[mm.sup.3]; hemoglobin, 48 g/L; hematocrit, 16.1%; white blood cells, 4.6 X [10.sup.3]/[mm.sup.3]; and platelets, 2.95 X [10.sup.5]/[mm.sup.3]. She had no abnormalities of her blood chemistry. An upper gastrointestinal tract endoscopy showed mucosal telangiectasia in the stomach and duodenal bulb. Celiac arterial angiography revealed marked dilation, tortuosity and a corkscrewlike appearance of the left hepatic arterial branches, pooling of the contrast medium in the venous phase, and early visualization of the hepatic veins, signifying A-V shunts. The right hepatic artery, originating from the superior mesenteric artery, showed the same findings. The diagnosis of HHT with hepatic involvement was made. Her severe anemia on admission was ascribed to repeated nasal and gastrointestinal bleeding.
A tumor (4 cm in diameter) in the hepatic hilus was revealed by abdominal ultrasonography and diagnosed as adenocarcinoma by an aspiration needle biopsy specimen. Her complaints on admission were attributable to this tumor A laparotomy revealed an unresectable tumor encasing the hepatic arteries, portal vein, and common bile duct in the hepatic hilus. Tortuous dilation of the hepatic arteries and capillary telangiectasia of the hepatic surface in the operative field were remarkable. Local irradiation of the tumor (2 Gy/d) was initiated, but had to be ceased because she developed obstructive cholangitis (she received a total of 14 Gy). Administration of 600 mg/d of doxifluridine (Furtulon, Nippon Roche Co Ltd, Tokyo, Japan) also had to be terminated because of severe anorexia (a total of 27 g was given).
One year after the diagnoses of HHT and bile duct cancer, she was readmitted with epigastralgia, abdominal distention, dyspnea, constipation, and anemia, and gastric endoscopy showed a benign open gastric ulcer (15 mm in diameter). She suddenly developed hepatic encephalopathy accompanied by stupor, hyperammonemia (1.98 mg/L), and the appearance of a slow-wave pattern on the electroencephalogram. The stupor was relieved by oral administration of lactulose and branched-chain amino acids (Aminoleban, Otsuka Pharmaceutical Co Ltd, Tokyo, Japan). Peritonitis carcinomatosa was diagnosed by the positive cytological result of the ascites. Abdominal computed tomography revealed a 7-cm-diameter mass in the pelvic cavity, and chest x-ray films showed pleural effusions and marked cardiomegaly with a cardiothoracic ratio of more than 0.70. Cardiac ultrasonography revealed severe tricuspid regurgitation, but good motion of the bilateral ventricular walls with a left ventricular ejection fraction of 0.78, suggesting congestive heart failure due to increased venous return through the intrahepatic A-V shunts. Unexpectedly, she developed left hemiplegia and right conjugate deviation, and brain computed tomography showed a large fresh infarction of the right frontal lobe. She experienced progressive oliguria and died 2 weeks after the cerebral infarction and 1 year 8 months after the diagnoses of HHT and bile duct cancer Autopsy was performed 7 hours postmortem.
The postmortem examination revealed a slightly icteric liver with marked vascular abnormalities and an adenocarcinoma of the common hepatic duct. Because the tumor showed extraductal extension, the common hepatic duct was mildly stenotic without causing obstructive jaundice. The hepatic arteries and their branches were markedly dilated and tortuous, whereas the portal and hepatic veins only showed mild dilation and thickening of the walls, as shown in Figure 1. Histologic examination revealed mild distortion of the lobular architecture, complex vascular abnormalities, and mild portal fibrosis (Figure 2). The hepatocytes showed atrophy, fatty changes, and cholestasis in the centrilobular areas, and slight focal lymphocytic infiltration was present in the portal areas. Multiple foci of ectatic sinusoids were present in the lobules, and the hepatic arterial branches showed marked angiomatous dilation and tortuosity with intimal hyperplasia in the portal areas. Some branches of the portal vein were also remarkably dilated and often emptied into ectatic sinusoids at the limiting plates.
The samples for 3-D reconstruction study were taken from the peripheral portion of the liver remote from the radiation field and bile duct cancer. The results of hepatic microvasculature are shown in Figure 3. The interlobular arteries gave off several arteriolar branches, some of which ran close and parallel to the limiting plates (periportal arterioles). Others entered the lobules (interlobular arterioles) and divided into capillaries. The periportal arterioles often communicated directly with the ectatic sinusoids, causing A-V shunts through the ectatic sinusoids (Figure 3, a and c). In contrast, the 3-D study of a healthy liver showed absence of this type of communication between arterioles and sinusoids. The ectatic sinusoids often originated from the dilated portal venous branches, forming significant P-V shunts (Figure 3, b and d). These connections between portal veins and sinusoids were seen in the healthy subject; however, they were more frequent and large in the HHT-involved liver No A-P shunts were identified in the HHT liver or the healthy liver.
The endothelium of the central veins, small portions of sinusoidal endothelium, and a few interstitial cells were positive for endoglin in the healthy livers by immunostaining (Figure 4); however, any kind of vascular endothelium was negative for endoglin in the HHT liver (data not shown).
No vascular abnormalities were found in the lung or skin of the patient, and neither esophageal varices nor splenomegaly suggestive of portal hypertension was present.
A 4-cm tumor arose from the common hepatic duct and directly invaded the pancreatic head and liver. The tumor encased the hepatic arteries and the portal vein without causing stenosis or occlusion. Neither cholangitis nor cholelithiasis occurred. The histologic type of the tumor was moderately differentiated adenocarcinoma. Peritonitis carcinomatosa with large amounts of dark yellow ascites (1100 mL) was observed, and a metastatic tumor (7 X 8 X 5 cm) was present in the Douglas pouch (Schnitzler metastasis). Microscopic metastasis to the lungs and extensive lymphogenous metastases to the intra-abdominal and supraclavicular nodes were present.
Examination of the heart, which weighed 300 g, revealed mild concentric hypertrophy, old anteroseptal subendocardial myocardial infarction, and nonbacterial thromboendocarditis of the aortic valve. A large fresh infarct, caused by thromboembolism from the heart, was found in the right frontal lobe (F2) of the brain. The direct causes of death were peritonitis carcinomatosa and cerebral infarction.
Recent studies by positional cloning approaches identified 2 causative genes of HHT: HHT1 and HHT2, which encode endoglin and activin receptor-like kinase 1 (ALK1), respectively. Therefore, HHT is genetically heterogenous. In fact, HHT1 gene mutations are frequently found in HHT patients with pulmonary fistulas, which are rare in patients without such mutations. The correlation between genotypes and phenotypes (clinical types), however, is still under investigation.
Endoglin is the most abundant transforming growth factor [Beta]--binding protein in endothelial cells, whereas ALK1 is a type 1 cell-surface receptor for the transforming growth factor [Beta] superfamily of ligands. Transforming growth factor [Beta] plays an important role in vascular remodeling by virtue of its effects on extracellular matrix production by endothelial cells, stromal interstitial cells, smooth muscle cells, and pericytes. High levels of both endoglin and ALK1 are expressed by endothelial cells and other highly vascularized tissues.
In our immunohistochemical study, endoglin is mainly expressed on the endothelium of central veins in the normal liver The present case seemed to be HHT1 because of the lack of endoglin immunoreactivity. Considering HHT is an autosomal dominant disorder, the chromosome of the patient should have both normal and mutated genes. Thus, decreased degree (half) of endoglin expression was expected in this case. Accordingly, the lack of immunoreactivity may imply low sensitivity of immunohistochemical method, rather than the total loss of endoglin expression. Regarding the endoglin expression pattern on liver tissues, it is difficult to understand how reduced endoglin expression located on the central vein could account for all the vascular abnormalities. Further investigation is necessary to correlate the functional abnormalities and morphological changes.
This study has shown that the essential pathologic changes of the hepatic vasculature in patients with HHT are as follows: (1) focal sinusoidal ectasia, (2) abnormal direct communications between hepatic arteriolar branches and ectatic sinusoids (formation of A-V shunts), and (3) frequent and large communications between the portal and central veins through ectatic sinusoids (formation of P-V shunts). `Dilation and tortuosity of hepatic arteries seem to be phenomena secondary to an increased blood flow. As for the hepatic arterial termination, previous studies and our 3-D study on a healthy liver disclosed the constant presence of intervening Capillaries between hepatic arteries and sinusoids.[8,9] Therefore, the direct communication between arterioles and ectatic sinusoids seen in this patient was definitely abnormal. A similar 3-D reconstruction study on cutaneous telangiectasia in HHT was previously reported. To our best knowledge, however, there have been no reports on 3-D reconstruction study of the hepatic lesions of HHT similar to ours. The clinical and angiographic findings in our patient were consistent with the results of the 3-D analysis. Namely, high-output congestive heart failure and hepatic encephalopathy suggested the presence of A-V and P-V shunts, respectively, and the presence of an intrahepatic A-V shunt was also indicated by angiography.
In conclusion, by means of 3-D analysis, we have succeeded in demonstrating the complicated hepatic microvasculature associated with HHT and unveiled the pathogenesis of the intrahepatic vascular shunts. Furthermore, the immunohistochemical study seems to be a useful tool for identification of HHT1.
We are grateful to all staffs of the Department of Pathology, Tokyo Metropolitan Geriatric Hospital, for the preparation of serial sections and immunohistochemical slides. References
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[4.] Martini GA. The liver in hereditary haemorrhagic teleangiectasia: an inborn error of vascular structure with multiple manifestations: a reappraisal. Gut. 1978; 19:531-537.
[5.] Daly JJ, Schiller AL. The liver in hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu disease). Am J Med. 1976;60:723-726.
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[7.] Bourdeau A, Cymerman U, Paquet ME, et al. Endoglin expression is reduced in normal vessels but still detectable in arteriovenous malformations of patients with hereditary hemorrhagic telangiectasia type 1. Am J Pathol. 2000;156:911-923.
[8.] Ohtani O, Murakami T, Jones AL. Microcirculation of the liver with special reference to the peribiliary portal system. In: Motta PM, DiDio LJA, eds. Developments in Gastroenterology Volume 2: Basic and Clinical Hepatology. The Hague, the Netherlands: Martinus Nijhoff Publishers; 1982: 85-96.
[9.] Yamamoto K, Sherman I, Phillips MJ, Fisher MM. Three-dimensional observations of the hepatic arterial terminations in rat, hamster and human liver by scanning electron microscopy of microvascular casts. Hepatology. 1985;5:452-456.
[10.] Braverman IM, Keh A, Jacobson BS. Ultrastructure and three-dimensional organization of the telangiectases of hereditary hemorrhagic telangiectasia. J Invest Dermatol. 1990;95:422-427.
Accepted for publication March 15, 2001.
From the Departments of Pathology (Drs Sawabe, Arai, and Esaki) and Internal Medicine (Drs Tsuru and Fukazawa), Tokyo Metropolitan Geriatric Hospital, and Department of Clinical Pathology, Tokyo Metropolitan Institute of Gerontology (Dr Takubo), Tokyo, Japan.
Reprints: Motoji Sawabe, MD, Department of Pathology, Tokyo Metropolitan Geriatric Hospital, 35-2 Sakae-cho, Itabashi, Tokyo 173-0015, Japan (e-mail: email@example.com).
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|Author:||Sawabe, Motoji; Arai, Tomio; Esaki, Yukiyoshi; Tsuru, Masanobu; Fukazawa, Toshio; Takubo, Kaiyo|
|Publication:||Archives of Pathology & Laboratory Medicine|
|Date:||Sep 1, 2001|
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